A “Rigid and flexible” molecular sieving membrane constructed by in-situ polymerization of COFs to repair defects in MOF membrane

MOF membrane supported on flexible substrates faces the issues of non-selective defects as well as poor mechanical compatibility. Herein, a “rigid and flexible” MOF/COF molecular sieving membrane is acquired by the in-situ polymerization of COFs among the inter-crystalline and interfacial defects in the MOF membrane. Taking advantage of different osmotic pressures on both sides of MOF membrane during the counter-diffusion process, the COFs monomers diffuse from bottom to top to the inter-crystalline and interfacial defects and meet with the catalyst for further polymerization and crystallization, thus repairing non-selective defects of the MOF membrane. In the MOF/COF membrane, COFs exhibit a strong adsorption affinity for CO 2 , which can slow down CO 2 permeation and enhance H 2 /CO 2 selectivity. Meanwhile, the in-situ polymerization of COFs primarily occurs at the inter-crystalline defects of MOF membrane and the interface between MOF membrane and polymer substrate, without forming a resistance layer on MOF membrane surface, which is demonstrated by the SEM and AFM results. Additionally, the counter-diffusion growth of COFs allows for the connection between the organic substrate and the inorganic MOFs layer through COFs, thereby improving the mechanical flexibility of MOF membrane confirmed by the mechanical properties. Besides, through regulating the polymerization process of TpPa-1 including time and monomer concentration, the H 2 /CO 2 separation of ZIF-67/TpPa-1 membrane can be tuned precisely. Therefore, the ZIF-67/TpPa-1–0.90 membrane at a polymerization time of 24 h presents H 2 permeance of 1114 GPU and H 2 /CO 2 selectivity of 17.52, an increase of 178.1 % compared to the pure ZIF-67 membrane, which is far beyond the 2008 upper bound and approaching the up-to-date data line. Together with the additional good mechanical properties, stability and universality, the proposed “rigid and flexible” MOF/COF molecular sieving membrane is promising in H 2 /CO 2 separation.